Outdoor swimming pools and associated equipment are commonly constructed to operate with a water level that must be maintained within close limits. During hot, dry, windy weather, evaporation may cause the water level to drop as much as one inch per day. Water must be added regularly to replace the amount that evaporates or splashes out of the pool during use, and for the great majority of existing pools, this filling operation is performed manually. Failure to fill the pool to the requisite operating water level, even for a brief period, may result in damage to the associated pump, heater, and filter.
During rainy weather, a pool tends to fill above the desired operating water level, and the excess water must be removed. This may be accomplished by allowing the filter pump to deliver excess water to the same drain that is used when the filter is backwashed or cleaned. This draining operation is most commonly controlled manually, usually during heavy rains, to assure that the water level is not permitted to drop too low.
A small number of pools constructed recently in accordance with new code requirements include automatic overflow systems for draining of excess water, but an insignificant number of existing pools have any provisions for both draining and filling the pool automatically under all operating conditions.
Various techniques for filling or draining a pool are described in the literature (see, for example, U.S. Pat. Nos. 2,739,939; 2,809,752; 3,386,197; 3,739,405; 3,895,402; 3,908,206; 3,997,925; and 4,211,249).
The retrofitting of an existing pool with equipment for automatically controlling the water level commonly involves expensive and undesirable reconstruction of the pool and surrounding decking.